Sensitivity of juvenile freshwater mussels (Lampsilis fasciola, Villosa iris) to total and un-ionized ammonia.

This study evaluated the sensitivity of juveniles of two freshwater unionid mussel species (Villosa iris [Lea] and Lampsilis fasciola [Rafinesquel) to un-ionized and total ammonia. Five concentrations of ammonium chloride were tested using 96-h static-renewal toxicity tests at 12 and 20 degrees C. Based on their respective mean 96-h lethal concentration to 50% (LC50s), V. iris (0.11 mg/ L NH3-N) was more sensitive than L. fasciola (0.26 mg/L NH3-N). At 96 h, significant differences in sensitivity to un-ionized ammonia between the two temperatures were not observed for either species. Comparison of LC50s reported for other aquatic organisms to the 96-h LC50s calculated for juvenile L. fasciola and V. iris shows these two mussel species to be among the most sensitive to un-ionized ammonia. Based on reported levels of un-ionized ammonia in the aquatic environment from anthropogenic sources, un-ionized ammonia may be an important limiting toxicological factor to freshwater mussel populations.